1. Field of the Invention
The present invention relates to a method of manufacturing a plasma display panel, and more particularly to a method of manufacturing a substrate with ribs for a plasma display panel.
2. Description of the Related Art
In general, ribs (also referred to as “barrier ribs”) for partitioning a discharge space of a conventional plasma display panel (hereinafter, PDP) are formed by a sandblasting method. The sandblasting method is performed as follows. On a substrate (for example, a rear substrate) on which electrodes and a dielectric layer to cover the electrodes for protecting them from the sandblasting are formed, a rib paste is applied to have a predetermined thickness and dried, thereby forming a rib material layer. Subsequently, a photosensitive dry film resist is applied on the rib material layer and then exposed to light and developed into a desired rib pattern, thereby forming a mask of the dry film resist. An abrasive is blasted onto the rib material layer via the mask of the dry film resist to remove a portion of the rib material layer exposed from the mask, thereby patterning the rib material layer into a predetermined shape. Thereafter, the mask is exfoliated by caustic soda and the resulting substrate is fired to burn out a synthetic resin contained in the rib material layer, thereby forming ribs.
However, a great number of steps are needed for forming the ribs by the sandblasting method as described above. In addition, the rib material layer thus formed is cut and discarded by more than half, so that use efficiency of the material layer is decreased and rib production costs are remarkably increased.
Japanese Unexamined Patent Publication No. 2000-21303 discloses an improved method of forming ribs on a rear substrate for a conventional PDP. This rib formation method is a transfer method for the formation of ribs in which the ribs are formed by molding a rib paste layer (rib material layer) using a mold. The transfer method includes the following steps. On a surface of a rear substrate 102 on which electrodes 121 are previously arranged (see FIG. 6(A)), a rib paste 123 is applied which contains a thermosetting or a UV-cured organic binder but does not contain a volatile solvent, to form a rib paste layer (see FIG. 6(B)). Then, air between the mold 124 and the rib paste layer 123 is expelled by degassing while a thin plate elastic mold 124 with cavities corresponding to a predetermined shape of the ribs is pressed against the rib paste layer 123 in order to improve adhesion therebetween (see FIG. 6(C)). Thereafter, the rib paste layer 123 is cured by heat or ultraviolet irradiation while pressing the mold against the layer 123 with a predetermined pressure via a cushion material 125 in order to mold ribs (green ribs) 123a, thereby integrally sticking the ribs 123a thus molded to the rear substrate 102 (see FIG. 6(D)), generating strength enough to resist releasing force. As a result, it is possible to surely mold on the rear substrate the ribs (green ribs) 123a having no defects of air bubbles and having a high level of height accuracy (see FIG. 6(E)). In this rib formation method, a dielectric layer covering the electrodes is formed along with the ribs.
In the conventional PDP, as described above, the dielectric layer is provided on the rear substrate after the formation of electrodes and before the formation of ribs. In such a conventional PDP, leads and terminals of the electrodes not covered with the dielectric layer are exposed. Therefore, during firing of the rib paste (green rib) and a phosphor paste and during fusing with a sealing material, the exposed portion of the terminals and leads is thermal-oxdized, which will cease conduction. One measure to solve such a problem may be to form a terminal protective layer by applying the rib paste on the leads and terminals at the formation of ribs. This measure, however, has a disadvantage that adhesion of the rib paste to the electrodes is not good. That is, because a firing temperature of the rib paste (green rib) is equal to or less than a softening temperature of glass contained in the rib paste, and for this reason, even if the rib paste (green rib) is fired, a glass material contained in the rib paste does not melt enough to flow liquidly, so that a gap is liable to occur at an interface between the electrodes and the rib paste. Thus, there is a problem that a leak (of discharge gas) may be caused by the gap at a periphery portion of panel assemblies sealed with the sealing material.
Further, it is necessary to perform etching of a portion of the terminal protective layer applied on a terminal portion after the assembly of a panel. However, since the rib paste contains a large amount of filler such as an alumina filler, the paste is hardly dissolved in acid such as nitric acid and it is difficult to etch away the portion of the terminal protective layer, which is problematic for the conventional PDP.